In certain types of electrical equipment, such as load centers, for example, it is desirable to have a circuit breaker for making and breaking circuits under controlled conditions as well as to interrupt circuits when overload conditions occur. In a load center having a molded case circuit breaker, the circuit breaker mounts into the enclosure and is keyed into a fixed position and is bolted to the electrical bus supplying power. Needless to say, in the enclosure space is at a premium. It is therefore desirable to provide ground fault circuit interruption protection in the load center in the space available. Traditionally, ground fault protection has been provided for these circuit breakers by providing a separately mounted ground fault relay which is then wired to the trip accessory on the circuit breaker. While this scheme works reasonably well, it requires additional space and the relay has to be mounted remotely from the circuit breaker which requires extra time and materials which increase cost. Also, this method is not well suited for field installation.
Another scheme uses a separately mounted ground fault relay and coil remote from a circuit breaker which are connected to a circuit breaker that is equipped with a shunt trip accessory. U.S. Pat. No. 4,209,760 which issued to Bernard DiMarco et al on June 24, 1980 and U.S. Pat. No. 4,112,270 which issued to T. J. Rys on Sept. 5, 1978 disclose circuit breakers with accessories. DiMarco discloses a multi-pole circuit breaker which has a molded insulating housing which defines an external cavity in which an shunt trip assembly is removably mounted. The shunt trip assembly includes an electromagnet with an operating member which engages the cradle latch to release the latter and automatically trip the circuit breaker. When ground fault protection is desired a ground fault relay signals the shunt trip assembly and causes the circuit breaker to trip. Again this requires additional parts, is costly and requires labor and is not the sort of thing that lends itself to installation in the field.
Rys discloses a single pole circuit breaker module constructed so that its housing is provided with frangible sections aligned with the pivot pins for the contact arm, the cradle and the operating mechanism latch. These pins are keyed to the elements mounted theron and each pin is provided with a formation to engage a complementary formation projecting sideways from the auxiliary feature module. In the case of a shunt trip auxiliary module the solenoid operated member thereof is operatively connected to the pivot for the circuit breaker latch whereby actuation of the shunt trip solenoid serves to move the latch to its unlatched position for tripping of the circuit breaker. Again, however, extra parts and space are required to provide ground fault protection. It is desirable to provide ground fault protection ulitizing the existing space.
There are circuit breakers that have ground fault circuit protection built as an integral part of the breaker. However this type of breaker necessarily is more expensive and bulkier than a standard breaker without the ground fault circuit protection. It is desirable to have a simple circuit breaker to which a ground fault accessory could be added in the field. This arrangement would allow a user to install the circuit breaker and add the ground fault protection when needed as convenient. Again however, space constraints are critical and must be taken into account when accessories are added.
A bolt-on accessory for a molded case circuit breaker does exist which can be added in the field in the very limited space constraints of a load center. However, this accessory only has a shunt trip accessory, not a ground fault accessory. Thus, the problem again presents itself that there is no available ground fault bolt-on accessory available. For a motor controller the shunt trip accessory is more or less a necessity because the shunt trip accessory usually includes an under voltage relay and other features which are desirable in a load center. Thus, even if a ground fault accessory were available in the same size package as the shunt trip accessory, there still would not be enough room in the load center for the addition of both the shunt trip and the ground fault relay. What is needed is a bolt-on accessory containing both the ground fault and shunt trip protection. It is desirable to have the ground fault and the shunt trip protection available in the same accessory.
The present invention is directed to overcoming one or more of the problems set forth above.